It is frequently desirable to sense a voltage and convert it into a current signal. One particular example is in sensing a current level where a voltage sensed across a current sensing resistor is converted into a current signal to drive protective or alarm circuitry. Typically, the transconductance function is performed by a transconductance amplifier circuit utilizing an operational amplifier. Since the sensing voltage across the small impedance of the sensing resistor is generally very small (i.e., low millivolt range) the operational amplifier must be carefully trimmed to eliminate any error-inducing effect that its offset voltage characteristic might cause. The trimming techniques utilized to eliminate the offset voltages add considerably to the expense of the operational amplifier. A further complication introduced by using an operational amplifier is a bias arrangement requirement of two voltages of opposite polarity as the bias source for the operational amplifier.